You Really Do Have Some Expectation of Privacy in Public

Being out in the world advocating for privacy often means having to face a chorus of naysayers and nihilists. When we spend time fighting the expansion of Automated License Plate Readers capable of tracking cars as they move, or the growing ubiquity of both public and private surveillance cameras, we often hear a familiar refrain: “you don’t have an expectation of privacy in public.” This is not true. In the United States, you do have some expectation of privacy—even in public—and it’s important to stand up and protect that right.

How is it possible to have an expectation of privacy in public? The answer lies in the rise of increasingly advanced surveillance technology. When you are out in the world, of course you are going to be seen, so your presence will be recorded in one way or another. There’s nothing stopping a person from observing you if they’re standing across the street. If law enforcement has decided to investigate you, they can physically follow you. If you go to the bank or visit a courthouse, it’s reasonable to assume you’ll end up on their individual video security system.

But our ever-growing network of sophisticated surveillance technology has fundamentally transformed what it means to be observed in public. Today’s technology can effortlessly track your location over time, collect sensitive, intimate information about you, and keep a retrospective record of this data that may be stored for months, years, or indefinitely. This data can be collected for any purpose, or even for none at all. And taken in the aggregate, this data can paint a detailed picture of your daily life—a picture that is more cheaply and easily accessed by the government than ever before.

Because of this, we’re at risk of exposing more information about ourselves in public than we were in decades past. This, in turn, affects how we think about privacy in public. While your expectation of privacy is certainly different in public than it would be in your private home, there is no legal rule that says you lose all expectation of privacy whenever you’re in a public place. To the contrary, the U.S. Supreme Court has emphasized since the 1960’s that “what [one] seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.” The Fourth Amendment protects “people, not places.”  U.S. privacy law instead typically asks whether your expectation of privacy is something society considers “reasonable.”

This is where mass surveillance comes in. While it is unreasonable to assume that everything you do in public will be kept private from prying eyes, there is a real expectation that when you travel throughout town over the course of a day—running errands, seeing a doctor, going to or from work, attending a protest—that the entirety of your movements is not being precisely tracked, stored by a single entity, and freely shared with the government. In other words, you have a reasonable expectation of privacy in at least some of the uniquely sensitive and revealing information collected by surveillance technology, although courts and legislatures are still working out the precise contours of what that includes.

In 2018, the U.S. Supreme Court decided a landmark case on this subject, Carpenter v. United States. In Carpenter, the court recognized that you have a reasonable expectation of privacy in the whole of your physical movements, including your movements in public. It therefore held that the defendant had an expectation of privacy in 127 days worth of accumulated historical cell site location information (CSLI). The records that make up CSLI data can provide a comprehensive chronicle of your movements over an extended period of time by using the cell site location information from your phone.  Accessing this information intrudes on your private sphere, and the Fourth Amendment ordinarily requires the government to obtain a warrant in order to do so.

Importantly, you retain this expectation of privacy even when those records are collected while you’re in public. In coming to its holding, the Carpenter court wished to preserve “the degree of privacy against government that existed when the Fourth Amendment was adopted.” Historically, we have not expected the government to secretly catalogue and monitor all of our movements over time, even when we travel in public. Allowing the government to access cell site location information contravenes that expectation. The court stressed that these accumulated records reveal not only a person’s particular public movements, but also their “familial, political, professional, religious, and sexual associations.”

As Chief Justice John Roberts